WO2013127759A2

WO2013127759A2 - Washout preventer

Info

Publication number: WO2013127759A2
Application number: PCT/EP2013/053765
Authority: WO
Inventors: David Brown
Original assignee: Aker Subsea As
Priority date: 2012-02-27
Filing date: 2013-02-26
Publication date: 2013-09-06
Also published as: WO2013127759A3; NO334558B1; NO20120548A1

Abstract

A device for preventing soil wash out during subsea drilling is shown and described, having means for retaining the soil around a sub sea anchor foundation (7). The means comprises at least, one flap member (7') hingedly (11) mounted adjacent to the lateral walls of a subsea anchor foundation (7) and adapted to receive a well bay insert (8). The flap member (7") is adapted to be in a substantially vertical position during the lowering to the seabed and remain in substantially horizontal position, parallel to the sea bed (2) during drilling operation and acts as a lid or a lock for physically holding the soil in position.

Description

WASHOUT PREVENTER

FIELD OF THE INVENTION

The present invention in general, relates to a wash out preventer for preventing collapse of top soil in the critical zone, during subsea drilling operation. More specifically, the present invention relates to a device for preventing soil wash out during subsea drilling, having at least one flap member attached in the region of the lateral walls of an anchor foundation, for retaining the soil around the anchor foundation. More particularly, the present invention relates to a device for preventing soil wash out during subsea drilling, according to the preamble of claim 1.

TECHNICAL BACKGROUND OF THE INVENTION Typically, well head systems for subsea exploration comprises a well head having a well head housing secured to the well casing. A blow out preventer is located on top the well head and a Christmas tree may or may not be position in between the well head have and the blow out preventer. The well template supports the well heads, while subsea suction anchor foundations support the well template and other subsea structures.

Usually, subsea anchor foundations comprise four vertical cylindrical structures. More recently, such anchor foundations have been developed as a single cylinder instead of four, often commonly known as a monobucket. Subsea anchor foundations normally support a template and well bay inserts for up to four wells. During subsea drilling operation wash out of top soil on the sea bed is often encountered during the initial drilling of the sea bed, up to a depth of around 10 to 20 metres. This wash out is usually caused by the pressure from the drilling mud, physically forcing the sea bed soil structure out of the drilled hole. It works like a pressure washer and blasts the soil out. This is indeed a challenge during drilling operations, because the seabed down to around 20 metres depth largely comprises unconsolidated loose formation.

Such wash out may also occur when large volumes of fluid, in the order of 2000 and 5000 litres per minute flushes out of the drill hole.

The end result of wash out during the first 10 to 20 metres of drilling is a conical hole into the soil with top diameter of up to around 7-8 metres.

It is also common experience during drilling operations that such a conical hole is a dreaded threat to the stability of the subsea anchor foundations and consequently to the well template, often rendering the entire installation as described hereinbefore invalid. Collapse of the template is an extreme eventuality.

Hence, prior art in this field has witnessed several attempts to retain this top soil during drilling operations. However, such devices are often found to have a complicated construction having a substantial number of components, resulting in cumbersome and costly installation.

Furthermore, hitherto, prior art technology has not focussed on developing a simple device, which is adapted to function in absolutely close proximity to the subsea anchor foundations and around the well bay inserts, so that soil retention around such foundations is achieved.

For example, WO2004018830 discloses a device for preventing such wash out which comprises modification of the drill stem so that it comprises a number of drill pipes. Each drill pipe has an inner central pipe and an outer pipe so as to have an annular space there between. The annular space is arranged to transport return fluid out of the bore hole. This document teaches a device which has the disadvantages as stated in the preceding two paragraphs.

N0139231 is another example of a subsea drilling template. Here the template is a very heavy structure that is intended to lie stable on the seabed substantially by its own weight. In addition the template has been provided with support legs that are folded out when the template has reached the seabed. The legs provide the template with an increased surface, which acts to further stabilize the template.

However, despite the support legs, the template still needs to be heavy and large. It therefore requires a large crane and crane ship to be deployed.

Accordingly, there is a long felt need for a device for preventing soil wash out during subsea drilling which apart from being simple is adapted to function in absolutely close proximity to the subsea anchor foundations and around the well bay inserts, so that soil retention around such foundations is achieved.

It is also known that large area, i.e. large horizontal area, surfaces (as is a likely solution for preventing washout) are very difficult to enter through the splash zone (i.e. the zone of initial intermittent contact with the sea surface), such as the one described in N0139231. The critical parameter involved in splash zone calculations increases with area (as a factor of weight) and increases with wave height. This results in large area structures being very limited in operation window when launching through the splash zone. Reduced exposed area increases the operational window. Hence the need arises to find a method to reduce exposed area when launching through the splash zone, whilst still enabling prevention of washout, as mentioned previously. Hence, there is also a need for a device for preventing soil wash out during subsea drilling which is adapted to be lowered with ease through the splash zone. The present invention meets the aforesaid long felt needs and other needs associated therewith.

OBJECTS OF THE INVENTION

It is the principal object of the present invention to provide a device for preventing soil wash out during subsea drilling which apart from being simple is adapted to function in absolutely close proximity to the subsea anchor foundations and around the well bay inserts, so that soil retention around such foundations is achieved.

It is another object of the present invention to provide a device for preventing soil wash out during subsea drilling which is adapted to be lowered with ease through the splash zone.

It is another object of the present invention to provide a device for preventing soil wash out during subsea drilling which is adapted to have minimum projected area to the sea surface through the splash zone and also during the following descent to the sea bed.

It is a further object of the present invention to provide a device for preventing soil wash out during subsea drilling which is adapted to operate in extreme weather conditions, thereby reducing drilling time and cost It is another object of the present invention to provide a device for preventing soil wash out during subsea drilling which is adapted to act as a substantially horizontal structure at sea bed surrounding the well bay insert to stop wash out. It is another object of the present invention to provide a device for preventing soil wash out during subsea drilling which is adapted to be lowered by an ROV and/or by wire and winch to the seabed. It is another object of the present invention to provide a subsea anchor foundation adapted to support a subsea structure such as a template, which is operatively associated in close proximity with a device for preventing soil wash out during subsea drilling, which device fulfills some or all of the objects as described hereinbefore.

How the foregoing objects are achieved and some other advantageous features, still not disclosed in prior art, will be clear from the following non- limiting description. All throughout the specification including the claims, the words, "subsea", "flap member/flap", "drill bit", "drill stem", "anchor foundation", "template", "well bay insert", "well bay" are to be interpreted in the broadest sense of the respective terms and includes all similar items in the field known by other terms, as may be clear to persons skilled in the art Restriction/limitation, if any, referred to in the specification, is solely by way of example and understanding the present invention.

SUMMARY OF THE INVENTION According to a first aspect of the present invention there is disclosed a device for preventing soil wash out during subsea drilling, having means for retaining the soil around the anchor foundation. According to the present invention the means comprises at least one flap member, hingedly fixed in the region adjacent to the lateral walls of a subsea anchor foundation and around the well bay insert so as to remain substantially parallel to the sea bed surface during drilling operation. Hence, it acts as a lid or a lock for physically holding the soil in position. Preferably the flap member is hinged along the lateral walls of an anchor foundation around a well bay insert.

More preferably, the flap member is hinged under the structure supporting the well bay insert adjacent to the lateral walls of the foundation.

According to another preferred embodiment the flap member is adapted to remain substantially parallel to the travelling direction and preferably along the lateral walls of the foundation or its portions are folded vertically together like butterfly wings under the well bay insert, during lowering through the water .

Preferably, the flap member, when horizontal to sea bed, is adapted to be vertically adjusted by means of a slot arrangement with respect to the sea bed in order to match the seabed profile and ensure maximum contact with the sea bed.

More preferably, the flap member is fixed on the well bay insert by means of a screw arrangement so as to be parallel with the sea bed, prior to beginning of the drilling operation.

Most preferably, the flap member has a circular or rectangular or cubical or folded profile or is substantially flat with a downward turned flange.

According to a second aspect of the present invention there is provided a subsea anchor foundation adapted to support a subsea structure such as a template, the subsea anchor foundation being operatively associated with a device according to the first aspect of the present invention.

Preferably, the anchor foundation is a mono bucket type foundation.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES Having described the main features of the invention above, a more detailed and non-limiting description of some preferred embodiments will be given in the following with reference to the drawings, in which: Figure 1 is a schematic longitudinal section of a typical soil formation along which drilling is carried out on the sea bed.

Figure 2 illustrates an eventuality when the bore hole is washed out during drilling.

Figure 3 illustrates a preferred embodiment of the device according to the present invention with the flap vertical to the sea bed.

Figure 4 illustrates the device of figure 3 with the flap disposed substantially parallel to the sea bed.

Figure 5 illustrates an enlarged detail view of the device shown in figure 4.

Figure 6 illustrates an enlarged detail front view of the device shown in figures 3, 4 & 5, with the flap laid in vertical position.

Figure 7a illustrates a schematically another preferred embodiment of the device according to the present invention with the flap attached to the side walls of a monobucket and in a parked position.

Figure 7b illustrates the device shown in figure 7a with the flap opening for operation.

Figure 7c illustrates the device shown in figure 7a with the flap in open condition, ready for operation.

Figure 8a illustrates schematically the preferred embodiment of the device shown in figures 3 to 5 with the flap attached to the side walls of a monobucket and in parked condition. Figure 8b illustrates the device shown in figure 8(a) with the flap opening for operation. Figure 8c illustrates the device shown in figure 8a with the flap in open condition, ready for operation.

Figure 9a illustrates schematically another preferred embodiment of the device according to the present invention with the flap attached to the side walls of a monobucket and opening for operation.

Figure 9b illustrates the device shown in figure 9a with the flap in open condition ready for operation. DETAILED DESCRIPTION OF THE INVENTION

The following provides a detailed non-limiting description of some preferred embodiments of the present invention, which are purely exemplary. The drilling of a bore hole on the sea bed 2 is shown in figures 1 and 2. These two figures are not consequential to the present invention and have been included from the prior art acknowledged just for explaining the problem the present invention proposes to solve. The shaded area in figure 1 indicates the critical zone 3 close to the bore hole, which is prone to wash out This indicates the first 10 to 20 metres in the unconsolidated soil formation 4. The figure 1 shows the drill stem 5 and also the drill bit 6 and the template 1. Figure 2 shows the end result of a wash out due to large volumes of fluid flushing out from the bore hole. This fluid may be the drilling mud. The wash out zone is a substantially conical hole as shown, with a top diameter of say around 7 to 8 metres. The figure also shows the dislocation of the template 1 due to caving in of a portion of the sea bed 2 in the loose formation zone 4.

As stated before, this happens primarily because the subsea suction anchor foundation supporting the template also gets destabilized, due to such wash out and caving in of soil.

This is exactly what the present invention is focused to prevent, that is, the object is to retain soil around the well bay insert next to the anchor. The solution of the present invention has not been proposed or conceived in prior art.

For the sake of understanding in a simplified manner, application of the present invention, on a single foundation/monobucket is shown. It should be understood to persons skilled in the art that the present invention is effectively applicable in respect of all types of subsea anchor foundations, supporting well templates and other subsea structures. Further, for the sake of simplicity in description, only one flap T has been shown. There may however be one or a plurality of such flaps 7' around the foundations and well bay inserts. In all the figures, like reference numerals represent like constructional features.

As shown in figure 3 the wash out preventer comprises a flap attached to the side wall of a monobucket 7 by means of a hinge joint 11. Of course, the flap T may be hinged either on the side wall of the monobucket as shown in figure 3 or under a structure 9, supporting the well bay insert 8. The monobucket 7 is preferably a suction anchor, but may also be an anchor that is intended to penetrate the seabed by applying a downwardly directed force on top of the anchor. Figure 3 indicates a position where the flap T is vertical to the sea bed 2. The flaps are hinged such that when lifting the monobucket 7 from the vessel (not shown) and lowering it through the splash zone (not shown), the flaps are in a stored position, folded vertically along the side wall of the bucket 7 as shown in figure 3 (also shown in figures 7a, 8a, 9a as discussed later) or folded vertically like wings under the well bay insert 8.

The advantage of the arrangement as stated in the preceding paragraph is to ensure a minimum projected area to the sea surface through the splash zone and also during the descent to the sea bed 2. The flap T has a central hole 7" for the well bay insert 8 and tail pipe 8' to pass through. It also assists the flap T so that it stays located during drilling operation. The exact shape of the central hole 7" is adjusted to match the geometry of the hinging. In general, it preferably is an elongated hole.

Once, in position on the sea bed 2, the flap T is opened either by using an underwater ROV or by use of wire and winch from the surface. The figure 4 shows the position when the flap T is ready to operate and is substantially parallel to the sea bed 2 to be drilled.

The hinge joint 11 as shown in figures 3 and 4 and also in the subsequent figures 5 and 6, may be provided with a slot 11' for the hinge pin 11. This ensures that the flap T first will be brought through a swinging movement for making it parallel to the sea bed 2 to be drilled, followed by a vertical adjustment and alignment, with the actual sea bed 2. The flap T may be slightly inclined relative to the horizontal to match the seabed profile and ensure maximum contact with the seabed 2. As shown in further details in the figures 4 and 5, the flap T is prevented from moving in a vertical direction, once it has been engaged by a three-point adjustment screw system 10, fixed to the well bay insert 8.

Figure 5 is an enlarged detailed view of figure 4 while, figure 6 shows for the sake of understanding the various components, the device from the underside.

The flaps T may be made fully flat or may be curved to match the outer profile of the monobucket diameter or may be flat with a downward turned flange, forming a shallow bucket. Figure 7a illustrates schematically another preferred embodiment of the flap 7' attached to the side walls of a monobucket 7 in parked condition. The flap T is here rectangular. Figure 7(b) illustrates the flap T as it is being lifted for operation. Figure 7c illustrates the flap T shown in figure 7a in fully lifted condition, ready for operation.

Figure 8a illustrates schematically the preferred embodiment of the flap T shown in figures 3 to 5 attached to the side walls of a monobucket 7, in parked condition. Figure 8b illustrates the flap T as it is being lifted for operation. Figure 8c illustrates the flap shown in figure 8a in fully lifted condition, ready for operation.

Figures 9a and 9b show an alternative embodiment where the flap T may be folded upon itself by a folding line, extending diametrically over the flap 7', similar to the wings of a butterfly when the device is being lowered through the water.

Figure 9a illustrates schematically the flap attached to the side walls of a monobucket 7 as it is being opened for operation.

Figure 9b illustrates schematically the flap 7', shown in figure 9a in an unfolded open condition, ready for operation. The simple construction as hereinbefore described retains the soil around the anchor 7, during the initial around 10 to 20 metres of drilling. The flap like feature T being substantially parallel to the sea bed 2 during drilling operation, and acting as a lid or a lock, thus physically holding the soil in position, under the pressure exerted by fluid. Furthermore, the flap provides a solid barrier by which any initial leakage or pathway of fluid is prevented. Thus the forming of a pathway to the sea is prevented and consequently, the chances of wash out are greatly reduced. Thus, the present invention provides a substantially horizontal structure at the seabed surrounding a well bay insert to prevent wash out. It also ensures minimum projected area to the sea surface through the splash zone during its installation. The reduction of projected area also allows a larger operational window and hence operation in more extreme weather, ultimately reducing the time required for installation and the cost.

From the foregoing description and also from the appended claims it would be clear to persons skilled in the art, that all the objectives of the present invention are achieved.

The present invention has been described with reference to some preferred embodiments and some drawings for the sake of understanding only and it should be clear to persons skilled in the art that the present invention includes all legitimate modifications within the ambit of what has been described hereinbefore and claimed in the appended claims.

Claims

1.

A device for preventing soil wash out during subsea drilling, having means for retaining soil, characterised in that said means comprises at least one substantially planar flap member (7') adapted to be positioned substantially parallel with the seabed and act as a lid or a lock for physically holding the soil in place, the flap member (7') having an aperture for a drill string to pass there through, and said flap member being attached to a subsea monobucket anchor foundation (7), such as a suction anchor, in a manner whereby the flap member (7') can be positioned in a first orientation with the main plane of the flap (7') parallel to the direction of travel when the anchor (7) is being lowered down to the seabed and whereby the flap member (7') can assume a second orientation with the main plane substantially parallel with the seabed when the anchor (7) has reached the seabed.

2.

The device according to claim 1, characterised in that said flap member (7') is hinged (11) along the lateral walls of the subsea anchor foundation (7).

3.

The device according to claim 1, characterised in that said flap member (7') is hinged to a structure (9) supporting a well bay insert (8) adjacent to the lateral walls of the subsea anchor foundation (7).

4.

The device according to any one of claims 2 or 3, characterised in that said flap member (7') is arranged to remain in a position with the main plane substantially parallel to and proximal to the lateral walls of the foundation (7) during installation through the water.

5.

The device according to any one of claims 2 or 3, characterised in that said flap has a folding line across its main plane and that the portions on each side of the folding line are folded vertically together like butterfly wings under during installation through the water.

6.

The device according to any one of the preceding claims, characterised in that said flap member (7'), when in a parallel orientation to the sea bed (2), is arranged to be vertically adjustable with respect to the sea bed (2) to adapt to the seabed profile and ensure optimal contact with the sea bed (2).

7.

The device according to any one of claims 3 to 6, characterised in that said flap member (7') is adapted to be fixated relative to the well bay insert (8) by means of an adjustment arrangement (10), such as a multiple of adjustment screws.

8.

The device according to any of the preceding claim 3 to 7, characterised in that said flap member (7') is provided with a central opening (7") for receiving the well bay insert (8).

9.

The device according to any of one of the preceding claims, characterised in that said flap member (7') has a circular or rectangular or cubical or folded shape and is substantially flat with a possible downward turned flange.